Just before his first birthday on July 22, his proud parents have released a picture showing George walking toward the camera.

William and Kate, both 32, chose a butterfly exhibit at London's Natural History Museum as the location for this photo, released in honor of their son's big milestone.

The pic shows a confident George making progress in a way only a 1-year-old can. Using his arms to steady himself, he is about to totter toward photographer John Stillwell, of the Press Association wire service in the U.K.

"He's quick on his feet," Stillwell tells PEOPLE. "He was walking towards me – I was kneeling down to take the picture and he was on top of me as soon as he started walking. He was very quick. He looked really steady on his feet."

Stillwell, who says he was "really honored to be asked to do it," was part of a small group, including some of the couple's staff, who quietly headed to the museum on the morning of July 2.

They chose the exhibit known as Sensational Butterflies for its colorful surroundings and its pleasant temperature. For an inquisitive little boy fascinated by new things, it was yet another eye-opener for the toddler.

"It's a tropical oasis in the center of London," says a spokeswoman for the museum. Kate became a patron of the museum last year, and earlier this summer, the royal couple and Prince Harry held a biannual meeting of their Charities Forum, the collection of their charities, there.

"That was a business-focus morning, but they wanted to come back and have some family time here," says the spokeswoman.

For more on Prince George's first year, pick up the new issue of PEOPLE, on newsstands now